GLM 5.1 API Pricing
Z.ai (GLM) · context window 205K · prices updated 2026-09-29
Where GLM 5.1 sits on price
At $4.40 per million output tokens, GLM 5.1 is a mid tier model — 2.0× the median output price of $2.20, which puts it cheaper than 37% and pricier than 63% of the models we track. It sits 16th cheapest of the 18 Z.ai (GLM) models we track. Output costs 3.1× input, the usual spread — trim both, starting with the answer length.
Cached input is 81% cheaper. On an input-heavy workload you need roughly a 31% cache-hit rate to take 25% off the input line — reachable for chatbots and agents that resend the same system prompt and history.
What real workloads cost on GLM 5.1
These three workloads are the ones teams actually run on a mid-priced model — a $4.40/1M model is not bought for the same job as one ten times the price.
| Workload | Per request | Per month |
|---|---|---|
| Support chatbot — 500 conversations/day (5K in / 1.4K out) Conversation history re-sent each turn — the classic prompt-caching win. | $0.0132 | $197 |
| Document pipeline — 10K docs/day (3K in / 500 out) Batch-friendly: no user waiting, so a ~50% batch discount usually applies. | $0.0064 | $1920 |
| Small app — 1K requests/day (500 in / 150 out) The baseline most side projects actually run at. | $0.0014 | $40.80 |
Model your exact traffic in the API cost calculator — it preloads GLM 5.1 with caching and batch options.
GLM 5.1 price history
Z.ai (GLM) last raised GLM 5.1's output price on Sep 29, 2026 (+45% per output token), from $0.9646/$3.03 to $1.40/$4.40 per 1M in/out. That is one of 7 repricings in the 58 days we have tracked it — worth knowing before you hard-code today's rate into a budget.
| Date | Input /1M | Output /1M | Output change |
|---|---|---|---|
| Aug 2, 2026 (tracking began) | $0.966 | $3.04 | — |
| Aug 6, 2026 | $0.952 | $2.99 | -1% |
| Aug 10, 2026 | $1.40 | $4.40 | +47% |
| Aug 15, 2026 | $0.966 | $3.04 | -31% |
| Aug 25, 2026 | $1.26 | $3.96 | +30% |
| Aug 30, 2026 | $0.966 | $3.04 | -23% |
| Sep 25, 2026 | $0.9646 | $3.03 | 0% |
| Sep 29, 2026 | $1.40 | $4.40 | +45% |
Change-points from our daily price snapshots (tracking since Aug 2, 2026; intraday moves between snapshots are not captured).
GLM 5.1 vs Qwen3.8 27B
The closest-priced alternative from another vendor is Qwen3.8 27B (Alibaba (Qwen)) — priced within a rounding error on output, with $1.36 less per million input tokens. When two models land this close on price, the decision is quality on your own workload, not the price sheet: run 50 real requests through both and compare.
See Qwen3.8 27B pricing →Cheaper alternatives
More Z.ai (GLM) models
Frequently asked questions
› How much does the GLM 5.1 API cost?
GLM 5.1 costs $1.40 per million input tokens and $4.40 per million output tokens, with cached input at $0.26 per million (81% cheaper). That works out to roughly 227,273 output tokens per dollar.
› What does the support chatbot workload cost on GLM 5.1?
Support chatbot — 500 conversations/day (5K in / 1.4K out) costs about $0.0132 per request and $197 per month on GLM 5.1. Conversation history re-sent each turn — the classic prompt-caching win.
› What does it cost to fill GLM 5.1's 205K context window?
Sending 205K of input in a single request costs $0.2867 at $1.40 per million tokens — before any output. With prompt caching that same fill drops to about $0.0532 on repeat requests. This is why large context windows are cheap to advertise and expensive to actually use.
› Is GLM 5.1 worth the price?
GLM 5.1 sits in the middle of the market (16 of 18 by price within Z.ai (GLM)). The honest test is a routing experiment: send the same 200 real requests to this model and to a tier below, and compare failure rate against the price gap — most teams find a majority of traffic never needed the pricier model.